Supplied-value arithmetic only
Circuit-Breaker Preliminary Input Checks
Check three basic inequalities for an already selected overcurrent protective device. This page does not choose a rating, MCB/MCCB type, B/C/D curve, trip settings, breaking category or selectivity.
Three preliminary comparisons
Arithmetic evaluated
The public Schneider Electrical Installation Guide explains these IEC-based overload and breaking-capacity comparisons and also notes the special tested backup/cascading case. This page requires every quantity explicitly and only reports whether the numerical inequalities hold.
Current IEC product and installation scopes
IEC 60364-4-43:2023 is the current fourth edition for protection against overcurrent and coordination of overcurrent-protection measures. IEC 60898-1:2015 with Amendment 1:2019 and Corrigendum 1:2020 applies to specified a.c. circuit-breakers for household and similar installations up to 440 V, 125 A and 25 kA. IEC 60947-2:2024, sixth edition, applies to low-voltage circuit-breakers intended for instructed or skilled persons within its voltage scope. These standards use different product contexts and short-circuit ratings; a current threshold alone cannot choose between them.
What is not checked
Passing all three boxes is not approval. Still verify system voltage/frequency and AC/DC duty, poles and neutral, maximum and minimum fault currents, automatic-disconnection time and earth-fault loop, conductor short-circuit thermal withstand and energy limitation, protective conductor and RCD/additional protection, inrush/start and nuisance tripping, adjustable settings, ambient/installation derating, isolation, coordination/selectivity/backup using tested manufacturer data, upstream/downstream equipment, local law and inspection/testing.
B/C/D letters are not selected from a load name. The exact starting-current envelope and required fault/disconnection performance must be checked against the selected device time-current bands. Likewise, selectivity cannot be established by a universal current ratio; use verified manufacturer tables/curves or a validated coordination study.
Checked example
IB=28 A, In=32 A, Iz=41 A, I₂=46.4 A, Ik,max=10 kA and applicable breaking capacity=15 kA pass all three numerical comparisons; the missing checks above still remain.
